Optical path design for scanning assembly in compact bar code readers

ABSTRACT

A compact retro-reflective module for use in electro-optical bar code readers includes components arranged to fold outgoing and incoming light along crossed optical paths. The module is convertible between generating one-dimensional and two-dimensional scan patterns to read bar code symbols.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 09/223,482, filed Dec. 30, 1998 now U.S.Pat. No. 6,491,222, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/048,418, filed Mar. 26, 1998, now U.S. Pat. No.6,114,712, which is a continuation-in-part of U.S. patent applicationSer. No. 08/727,944, filed Oct. 9, 1996 now abandoned. This applicationis also a continuation-in-part of U.S. patent application Ser. No.09/379,153, filed Aug. 23, 1999, now U.S. Pat. No. 6,283,372, which is adivision of U.S. patent application Ser. No. 09/167,880, filed Oct. 7,1998 now U.S. Pat. No. 6,412,697, which is a continuation of U.S. patentapplication Ser. No. 08/595,162, filed Feb. 1, 1996, now U.S. Pat. No.5,861,615, which is a continuation of U.S. patent application Ser. No.08/153,053, filed Nov. 17, 1993, now U.S. Pat. No. 5,504,316. Thisapplication is related to U.S. Pat. No. 5,821,521 and to U.S. Pat. No.5,705,799. All of said patents and applications are hereby incorporatedby reference herein.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The field of the invention relates to electro-optical readers orscanning systems, such as bar code symbol readers, and more particularlyto the optical path design in a scanning module for use in applicationsrequiring particularly compact bar code readers.

DESCRIPTION OF THE RELATED ART

Electro-optical readers, such as bar code symbol readers, are now verycommon. Typically, a bar code symbol comprises one or more rows of lightand dark regions, typically in the form of rectangles. The widths of thedark regions, i.e., the bars and/or the widths of the light regions,i.e., the spaces, between the bars encode information in the symbol.

A bar code symbol reader illuminates the symbol and senses lightreflected from the regions of differing light reflectivity to detect therelative widths and spacings of the regions and derive the encodedinformation. Bar code reading type data input systems improve theefficiency and accuracy of data input for a wide variety ofapplications. The ease of data input in such systems facilitates morefrequent and detailed data input, for example, to provide efficientinventories, tracking of work in progress, etc. To achieve theseadvantages, however, users or employees must be willing to consistentlyuse the readers. The readers therefore must be easy and convenient tooperate.

A variety of scanning systems is known. One particularly advantageoustype of reader is an optical scanner which scans a beam of light, suchas a laser beam, across the symbols. Laser scanner systems andcomponents of the type exemplified by U.S. Pat. No. 4,387,297 and No.4,760,248 which are owned by the assignee of the instant invention andare incorporated by reference herein have generally been designed toread indicia having parts of different light reflectivity, i.e., barcode symbols, particularly of the Universal Product Code (UPC) type, ata certain working range or reading distance from a handheld orstationary scanner.

A variety of mirror and motor configurations can be used to move thebeam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798discloses a rotating polygon having a planar mirror at each side, eachmirror tracing a scan line across the symbol. U.S. Pat. No. 4,387,297and No. 4,409,470 both employ a planar mirror which is repetitively andreciprocally driven in alternate circumferential directions about adrive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660discloses a multimirror construction composed of a generally concavemirror portion and a generally planar mirror portion. The multimirrorconstruction is repetitively reciprocally driven in alternativecircumferential directions about a drive shaft on which the multimirrorconstruction is mounted. All of the abovementioned U.S. patents areincorporated herein by reference.

In electro-optical scanners of the type discussed above, the “scanengine” including the laser source, the optics, the mirror structure,the drive to oscillate the mirror structure, the photodetector, and theassociated signal processing and decoding circuitry all add size andweight to the scanner. In applications involving protracted use, a largeheavy hand-held scanner can produce user fatigue. When use of thescanner produces fatigue or is in some other way inconvenient, the useris reluctant to operate the scanner. Any reluctance to consistently usethe scanner defeats the data gathering purposes for which such bar codesystems are intended. Also, a need exists for compact scanners to fitinto small compact devices, such as notebooks.

Thus, an ongoing objective of bar code reader development is tominiaturize the reader as much as possible, and a need still exists tofurther reduce the size and weight of the scan engine and to provide aparticularly convenient to use scanner. The mass of the movingcomponents should be as low as possible to minimize the power requiredto produce the scanning movement.

It is also desirable to modularize the scan engine so that a particularmodule can be used in a variety of different scanners. A need exists,however, to develop a particularly compact, lightweight module whichcontains all the necessary scanner components.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION

It is an object of the present invention to reduce the size and weightof components used to produce scanning motion of the light beam, and tocollect the reflected light.

A related object is to develop an electro-optical scanning system whichis both smaller and lighter in weight.

It is yet a further object to produce a module which may be manufacturedconveniently, and at low cost.

A related object is to provide a module which may be assembled easily.

FEATURES OF THE INVENTION

Briefly, and in general terms, the present invention provides aretro-reflective scan module in an electro-optical reader operative fordirecting a light beam to, and for detecting light reflected from, a barcode symbol to be read. The module includes a generally planar,rectangular support such as a printed circuit board, a light source suchas a laser, an optical element such as a curved collection mirror, areciprocally oscillatable scan mirror, and a sensor such as aphotodiode.

In a preferred embodiment, the laser beam from the laser passes throughan aperture in the collection mirror along a first optical path toimpinge on the scan mirror. Light collected by the collection mirror isdirected to the sensor along a second optical path. The laser beamimpinging on the scan mirror is swept along a third optical path to thesymbol for reflection therefrom. The reflected light impinging on thescan mirror is directed along a fourth optical path to the collectionmirror.

In accordance with the invention, the second and third paths cross,thereby resulting in a compact design in which the laser and the sensorare located away from each other at opposite end regions of the support.The compact module has the form factor of a rectangular parallelepipedhaving dimensions less than 20.6 mm×14.2 mm×11.4 mm.

In accordance with another feature of this invention, the laser beamemitted by the laser does not directly impinge on the scan mirror, butinstead, directly impinges on a fold mirror which reflects the laserbeam to the scan mirror. The fold mirror may be reciprocally oscillatedin order to obtain two-dimensional scanning of the symbol, or may not beoscillated in order to obtain one-dimensional scanning. When notoscillated, the fold mirror is effectively stationary and acts as afixed mirror. A drive for the fold mirror is selectively disabled inorder not to oscillate the fold mirror.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.Further features of the invention are set out in the appendedindependent claims, and further preferred features are set out in thedependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned view of an optical assembly according tothe invention;

FIG. 2a shows a side view of a gun-type scanner suitable for use withthe optical assembly of FIG. 1;

FIG. 2b is a front view of the scanner of FIG. 2a;

FIG. 2c is a plan view of the scanner of FIG. 2a;

FIG. 2d is an exemplary hand-held optical scanner, suitable for use withthe optical assembly of FIG. 1;

FIG. 2e is an exemplary hand-held combined computer terminal and opticalscanner, again suitable for use with the optical assembly of FIG. 1;

FIG. 3 shows an optical assembly from which a scanning beam exits at anon-90° angle;

FIG. 4 is a flow chart showing operation of the scanner of FIGS. 2a-c;

FIG. 5a shows a thin flexible band drive of known type;

FIG. 5b shows an improved thin flexible band;

FIG. 6 is an exploded view showing the mounting of the thin flexibleband of FIG. 5b;

FIG. 7 shows the components set out in FIG. 6 in assembled form;

FIG. 8 shows an optical assembly in a housing in cut-away form;

FIG. 9 shows a 2D scan motion scanner assembly;

FIG. 10 is a schematic plan view corresponding to FIG. 9;

FIG. 11 shows an alternative scan assembly configuration;

FIG. 12 is an end view corresponding to FIG. 11;

FIG. 13a illustrates the scanning plane in a conventional assembly;

FIG. 13b illustrates the scanning plane in an assembly of the type shownin FIG. 11;

FIG. 14 shows an alternative bar code reader housing;

FIG. 15 is a view similar to FIG. 10, but showing a more compact design;and

FIG. 16 is a view of another compact design similar to FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a low cost optical assembly, for creating a scanning laserbeam for use in a bar code reader.

The optical assembly comprises two essentially separate portions, the“static optics” 10 and the scanner motor drive 12, both mounted to acommon support or printed circuit board (PCB) 14. Before the structureof the assembly is described in detail, it may be helpful to provide abrief overview of the operation of the device. The light beam 16 from asemiconductor laser 18 passes through a molded plastics lens 20 and isturned through 90° by total internal reflection from a prism 22. Afterexiting the prism, the beam passes through an aperture 24 in a collectormirror 26, and impinges onto an oscillating scanning mirror 28. Thisproduces a scanning outgoing light beam 30, which is directed toward anindicia (not shown) to be read. Although the mirror 28 is shown as beingangled, this is merely a drawing representation to render the shape andoperation of the mirror clearer. The mirror sweeps a beam in the planeof the paper on which the drawing is presented, and orthogonal to thePCB 14.

Reflected light 32 from the indicia is first received by the scanningmirror 28, which directs it onto a concave surface 34 of the collectormirror 26. This focuses the light via an aperture 36 and a filter 38onto a photodetector 40. The photodetector output signal is then passedon to suitable electronics within the PCB 14 by an electrical coupling42.

The scanning mirror 28 is mounted at 44 for oscillation about an axis,this being achieved by virtue of the interaction between a permanentmagnet 46 and a driven electromagnetic coil 48. A suitable drivingsignal is applied to the coil, via the PCB 14 and coil electricalcontact 50. The scanner motor drive 12 shown in FIG. 1 is exemplary, andmay be replaced with any type of mechanism for effecting a scanningmotion of the laser beam in one or two dimensions. For example, thescanner motor drive could comprise any of the configurations disclosedin U.S. Pat. No. 5,581,067 and No. 5,367,151, both of which areincorporated by reference. In this way, the static optics assembly 10may be used as a component in a variety of scanner designs.

Although a light masking aperture 36 may be used in front of thephotodetector 40, as shown in FIG. 1, for increasing the depth of focusof the photodetector, the same effect can be achieved without anaperture by appropriately specifying the area of the photodetector 40itself.

Another key feature of the invention is that the aperture 24 is locatedin a position in the collector mirror 26 so that the beam path of theoutgoing laser beam striking the mirror 28 is offset from the opticalaxis of the reflected light from the concave surface 34 of the collectormirror 26. In particular, the aperture 24 is located below the opticalaxis of the collector mirror 26, as shown in FIG. 1 (and in thecorresponding components in FIG. 11).

The important consequence of such design placement of the outgoing andreturn beam paths is that it permits an internal placement of theassembly in a compact housing configuration as that shown in FIG. 2d, inwhich the assembly of FIG. 1 is mounted on a printed circuit board (PCB)214 with the outgoing beam parallel to the plane of the PCB. Note alsothat the assembly is situated in the housing so that the outgoing beamis substantially orthogonal to the surface of the window 218. The window218 is depicted in the figure as being substantially perpendicular tothe PCB 214 and flush with the outer surface of the housing 210. Thesame positioning of the window is illustrated in another configurationin the embodiment of FIG. 2e. Such mechanical designs are easy tomanufacture, and enable a very compact reader to be designed.

Situating the window orthogonal to the outgoing laser beam, however,results in partial internal reflection of the outgoing light back in thesame direction and therefore into the assembly. The possibility of usingsuch a window and module configuration with the optical assemblies inthe prior art would be counter to good design for optimum performancesince in such configurations the reflected light from the window wouldbe captured by the light collecting portion and directed to thephotodetector, where it would be detected together with the returningreflected light from the bar code symbol, and create a very noisysignal. If the amount of reflection were substantial, the light couldeven flood the photodetector and overpower the signal of the returningreflected light from the bar code symbol. Bar code readers utilizingsuch modules or optical assemblies with prior art optical path designswould avoid such difficulties by typically utilizing a window that wasmounted at an acute angle with respect to the outgoing laser beam (see,for example, the placement of the windows in the bar code readersdepicted in U.S. Pat. No. 4,387,297; No. 4,409,470; No. 4,816,660; andNo. 5,280,164). Any internal reflection from such tilted windows wouldbe in a direction away from the optical assembly, thereby reducing thenoise of the signal received by the photodetector. Such tilted windowconfigurations require, however, more effort to implement mechanically,and increase the overall size of the housing.

The design of the optical path in the scan module according to thepresent invention permits the scan module to be mounted on a PCB, suchas shown in FIG. 2d, so that the window can be placed flush with thesurface of the housing and consequently orthogonal to the emitted laserbeam. The scan module could also be mounted flush against the window foran even more compact arrangement. Although reflected light from thewindow is returned in the direction of the beam path of the outgoinglaser beam, in the optical path design of the assembly of FIG. 1 theoutgoing laser beam optical path is different from the optical axis ofthe reflected light from the light collecting portion. Thus, suchinternally reflected light would not be directed by the light collectingportion to the photodetector 40, and therefore would not affect thesignal from the light reflected by the bar code symbol.

The implementation of the above-described offset outgoing and returnlight paths does not require the use of an apertured collector mirror26. The laser light source and the photodetector must be positioned withrespect to one another simply so that the emitted light beam partiallyreflected by the window and reflected by the light-collecting portiondoes not illuminate the photodetector, i.e., by having spaced-apart, oroffset, optical axes.

The optical assembly shown in FIG. 1 may be incorporated within any typeof fixed or portable optical scanner, for example, the scan-type scannerof FIGS. 2a-c, the hand-held scanner shown in FIG. 2d, or the hand-heldcomputer terminal/scanner shown in FIG. 2e.

Referring to FIGS. 2a to 2 c, a hand-held, gun-type scanner of ergonomicdesign is shown. The scanner includes a scanner body designatedgenerally 100 including a handle portion 102 and a head portion 104. Thehandle portion 102 is configured to be held upright in the user's palmand has a forward portion including a trigger 106 positioned preferablyto be operable by the user's forefinger. The head portion 104 isprovided at the top of the handle portion 102 and includes a front faceincluding a scanning window 108 and a bulbous rear portion extendingrearwardly from the handle 102 to rest on or above the user's hand inuse.

The scanner 100 is pivotably fixed to a base portion 110 about a pivotaxis 112 provided at the lower end of the handle 102. The base includesa flat bottom face 114 and extends outwardly from the handle portionboth forward and rear and to the sides such that the assembly as a wholecan be placed freestanding stably on a supporting surface. The scanner100 is arranged to pivot on the base 110 in the forward/backwarddirection. The base 100 provides an interface between the scanner 100and a host (not shown) by a cable 116. The cable 116 can simply carrypower or can also include a data path either for control information tobe passed to the scanner or for data ready to be downloaded to the hostfrom the scanner 100.

The base 110 includes on its underside 114 a pressure switch of anysuitable known type (not shown), release of which indicates to aprocessor in the scanner that the scanner is being operated in hand-heldmode. Accordingly the scanner switches to triggered mode indicating thatreading will only take place when trigger 106 is activated.

The control system is illustrated in more detail in the flow chart ofFIG. 4. It will be seen that a continuous loop is maintained by asuitable controller establishing whether or not the pressure switch isactivated (step 150). If the pressure switch is deactivated, thentriggered (hand-held) mode is entered (step 152); further discussion ofrelevant features may be found in U.S. Pat. No. 5,151,581, incorporatedherein by reference.

In the alternative mode, where the pressure switch is activated,continuous scanning (hands-free) mode 154 is entered. In this mode, apresentation scan pattern is always activated allowing all items to passin front of the scanner to be scanned. This can be used, for example, ata retail sales point such as a checkout stand. Accordingly thearrangement allows dual mode operation.

The scanner 100 shown in FIG. 2a-c is an omnidirectional scanner but thegun-type configuration provides the benefits of a conventionalone-dimensional scanner.

In addition, the adjustable angle provided by the incorporation of apivot axis 112 allows the scanner as a whole to be positioned at anydesired pivot angle for ease of reading and also allows the base to beangled to a comfortable position when in hand-held mode.

The main body 100 and base 110 are preferably modular such that one orother components can be changed at minimum expense to arrive at, forexample, a cordless embodiment. Optionally a mode button 118 isadditionally provided on the upper face of the head 104 (see FIG. 2c)allowing the user to select a scanning pattern of any desired type, forexample, based on the bar code symbols or other indicia to be read, orthe scanning conditions. In addition indicator lights such as LEDs areprovided at 120 which can indicate, for example, the mode of operationof the scanner, whether it is in hands-free or hand-held mode, and soforth.

Referring now to FIG. 2d, reference numeral 210 generally identifies ahand-held scanner in an alternative embodiment. The scanner mayalternatively be gun-shaped, or any suitable configuration may be used.The scanner is manually operable, for example, by a trigger (not shown).As known from the above-identified patents and applications incorporatedby reference herein, a light source component, typically but notnecessarily a laser, is mounted inside the scanner shown at block 210.The light source emits a light beam along a transmission path whichextends outwardly through a window 218 that faces indicia, e.g., barcode symbols, to be read. Also mounted within the block 210 is aphotodetector component, e.g., a photodiode, having a field of view, andoperative for collecting reflected light returning through the window214 along a path from the symbol.

The optical assembly of FIG. 1 is mounted within or as part of the block210.

In whichever scanner type the arrangement is provided, operation isgenerally the same. The photodetector generates an electrical analogsignal indicative of the variable intensity of the reflected light. Thisanalog signal is converted into a digital signal by an analog-to-digitalconverter circuit. This digital signal is decoded by a decode module222. The decode module 222 decodes the digital signal into datadescriptive of the symbol. An external host device 224, usually acomputer, serves mainly as a data storage in which the data generated bythe decode module 222 is stored for subsequent processing.

The block 210 and decoder 222 are mounted on a PCB 214. In operation,each time a user wishes to have a symbol read, the user aims the scannerat the symbol and pulls the trigger or otherwise initiates reading ofthe symbol. The trigger is an electrical switch that actuates the drivemeans. The symbol is repetitively scanned a plurality of times persecond, e.g., more than 100 times per second. As soon as the symbol hasbeen successfully decoded and read, the scanning action is automaticallyterminated, thereby enabling the scanner to be directed to the nextsymbol to be read in its respective turn.

In addition, the head need not be a portable hand-held type as fixedlymounted heads are also contemplated in this invention. Furthermore, theheads may have manually operated triggers, or may be continuouslyoperated by direct connection to an electrical source.

The oscillations need only last a second or so, since the multipleoscillations, rather than time, increase the probability of getting asuccessful decode for a symbol, even a poorly printed one. Theresonating reflector has a predetermined, predictable, known, generallyuniform, angular speed for increased system reliability.

Turning now to FIG. 2e, there is shown an alternative hand-held opticalscanner including additional features, this time taking the form of ascanning terminal 326. The terminal comprises a hand-held case 328having a data display screen 330 and a data input keypad 332. Theoptical assembly of FIG. 1, within the case 328, produces a scanninglight beam which extends outwardly through a window 334 which faces theindicia to be read. Light reflected from the indicia passes back throughthe window 334 and impinges on the photodetector component, for examplea photodiode, which creates a returning light output signal. Theinformation content within that signal may be stored in an on-boardmemory (not shown) or may be downloaded to a remote computer via a dataport 336. Alternatively, the information may be transmitted via a radiofrequency signal produced by an on-board radio transmitter/receiver 338.

In one embodiment the motor drive used to obtain scanning action ispreferably a “taut band element” drive. This type of drive is fullydescribed in, inter alia, U.S. Pat. No. 5,614,706 and No. 5,665,954which are commonly assigned herewith and incorporated herein byreference. In essence, the arrangement includes an optical element suchas a lightweight mirror mounted on a thin flexible strip (the “tautband”) mounted across an electromagnetic coil. A permanent magnet isattached to the optical element which interacts with a varying magneticfield created when an AC signal is applied to the coil to causerepetitive torsional motion in the flexible strip. As a result, theoptical element oscillates providing scanning motion.

FIG. 5a shows a taut band element drive of known type in more detail. Inparticular, coil 70, flexible strip 72, mirror 74 and permanent magnet76 can be seen. The flexible strip 72 can be held against the coil 70,for example, by a holding annulus 78. An AC voltage applied to the coilis represented schematically at 80 and causes torsional oscillationrepresented schematically by arrow 82. It will be apparent that thisarrangement can replace the arrangement shown generally in FIG. 1 asmirror 28 and drive arrangement 44, 46, 48 in a manner apparent to theskilled reader.

In a further embodiment shown in FIG. 5b, the flexible strip 72 isreplaced by an elongate element 84 which is V-shaped in cross-sectionperpendicular to its elongate axis on which is mounted the mirror 74 andpermanent magnet element 76. The V-shaped element 84 extends across acoil or is otherwise appropriately mounted in the same manner asprevious thin flexible element 72 and the permanent magnet 76 interactswith the AC magnetic field resulting in torsional deflection representedby arrow 86. The V-shaped cross-section of the band increases itsstiffness and in particular ensures that the torsional deflection isuniform or substantially uniform over the length of the band, the mirror74 being mounted on the apex of the “V”. It will be appreciated thatalternative configurations for the band cross-section can becontemplated such as X-, I-, H-, or W-shaped, as long as therequirements of torsional deflection and uniformity of that torsionaldeflection along the length of the band are maintained.

FIG. 6 shows in exploded form a practical mode of mounting the V-shapedelement 84 of FIG. 5b. Coil 70 is mounted on an E-configuration core 71a including a central arm 71 b which is received in the central recessof the coil 70 and outer arms 71 c and 71 d which extend to either sideof the coil and above it. A mounting plate 75 a is received on the outerarm 71 c, 71 d of the E-core and extends above and across the coil 70.The mounting plate 75 a includes a central aperture 75 b defining thespace across which the V-shaped element 84 extends. The V-shaped element84 includes limbs 84 a extending to either side of its longitudinal axissymmetrically at either end and the center and is mounted on themounting plate 75 a across the aperture 75 b in any suitable manner, forexample, by securing the end limbs 84 a to the upper face of themounting place 75 a. Cooperatingly configured V-shaped connectingelements 85 are secured to the V-shaped element 84 and generally alignedwith the limbs 84 a and the mirror 74 is mounted on the connectingelements 85 at the apex of the V-shaped element.

Depending from the mirror 74 is a yoke 73 also substantially of V-shapebut straddling the V-shaped element 84, having its outer ends 73 a, 73 battached to the rear of the mirror 74. The yoke 73 has a central portionwhich extends away from the mirror 74 and has lateral tabs 73 c, 73 d.The lateral tabs 73 c and 73 d are in register with the central limbs 84a, 84 b of the V-shaped element and are attached thereto. The permanentmagnet 76 is attached to the underside of the central portion of theyoke 73, for example, to the underside of the tabs 73 c and 73 d.Accordingly, the yoke 73 straddles the V-shaped element 84 such that thepermanent magnet projects over or through the aperture 75 b in themounting plate 75 a allowing optimum magnetic coupling with the coil 70.When an AC current is applied to the coil 70, the permanent magnet 76oscillates which in turn gives rise to torsional flexing of the V-shapedelement 84 and oscillation of the mirror 74. The assembled arrangementis shown in FIG. 7.

An assembled module incorporating the arrangement of FIG. 7 is shown inFIG. 8 in which it will be seen that a substantially cuboidal housing isincorporated. The direction of angular motion of the mirror is depictedby arrow A.

In another preferred embodiment, the type of motor drive used tooscillate the scan mirror can be a Mylar™ leaf spring supporting anunbalanced mirror assembly. In FIGS. 11-12 the mirror assembly ismounted to a Mylar leaf spring which flexes as the permanent magnet isdriven by the AC coil imparting an oscillating force.

Yet a further alternative is a “micro-machined” mirror assembly asdiscussed in U.S. Pat. No. 6,102,294 and No. 6,059,188 according towhich the mirror is driven back and forth directly by a suitable drivemotor, preferably of very small dimension. Yet a further alternative isto use a mirror of known rotating polygon type as discussed in theintroduction in relation to U.S. Pat. No. 4,251,798 according to whichthe mirror comprises a solid body having a plurality of faces angled toone another. As the body rotates, the beam is scanned by successiverotating faces of the polygon body. In one embodiment the Mylar motorcan be used in an arrangement for one dimensional scanning while aV-shaped taut band element (described above) can be used fortwo-dimensional scanning, also as discussed in more detail below.

Turning now to the static optics assembly 10 shown in FIG. 1, it will benoted that the laser focusing lens 20, the laser aperture 24 and thecollection mirror 26 are all defined by a single molded plasticsmaterial member, shown in cross-hatching and indicated generally by thereference numeral 52. The molded member 52 further acts to house and tolocate the laser 18, the filter 38 and the photodetector 40.

The preferred laser 18 is a semiconductor laser is mounted byconventional through-hole techniques on the PCB. The photodiode ispreferably an SMD (“surface mounted device”) device as is the AC coilfor the Mylar leaf spring motor. This eliminates the need for standoffsand hand-soldering or sockets, as are used on prior art scanners.Typically, the laser will be a standard packaged edge emitting laser.For minimum cost, the laser focusing is not adjustable, and the laser issimply installed with its mounting flange in contact with a shouldermolded as part of the molded member. This will position the laseraccurately enough with respect to the molded focusing lens 20 to provideadequate performance within an inexpensive scanner. The fact that thefocusing lens is molded as part of the same component as the shoulder 54minimizes tolerance buildups that could otherwise cause improperfocusing.

The laser is held in place within the molded member 52 by means ofUV-curing cement. Since the plastics material of the molded member istransparent to UV-light, the cement may be cured by shining UV lightthrough the member into the cavity within which the laser is positioned.Cement may be applied to the laser 18, or to the molded member 52, withthe laser then being pushed into the cavity until it abuts thepositioning shoulder 54. The assembly may then be exposed to ultravioletlight for a few seconds, so curing the cement. If desired for higherperformance, this method of retaining the laser also allows for afocusing adjustment to be made. In this case, the laser is graduallyslid into the cavity while the output beam is being monitored. Whencorrect focus is achieved, the assembly is exposed to UV-light, thuscuring the cement and locking the assembly into place.

In the unadjusted assembly, it may be possible to eliminate the cementby spring-loading the laser up against the positioning shoulder 54, forexample, by means of a rubber or foam washer 56 between the PCB 14 andthe bottom of the laser 18.

As shown in the drawing, the laser 18 has downwardly-extendingelectrical leads 58 which are simply installed directly into the PCB 14.This eliminates hand-soldering, but soldering could be used if desired.

The fact that the leads extend downwardly into the circuit board meansthat in a conventional laser, the beam will be directly upwardlyperpendicular to the board. The prism 22, previously described, ismolded into the top of the molded member 52 to direct the vertical laserbeam through the aperture 24 in the collector mirror 26 towards thescanning mirror 28. The prism 22 uses total internal reflection toreflect the laser beam, so it is not necessary to coat the upper surfacewith a reflective coating.

To provide for further focusing of the laser beam, should it be desired,it would also be possible to shape the exit surface 60 of the prism.

It is desirable that, somewhere along its path, the laser beam shouldpass through a beam stop. The aperture 24 in the collector mirror 26 mayserve this purpose. Alternatively, the lens 20 or the reflecting or exitsurface of the prism 22 could provide the beam stop.

In fact it is preferred to keep the aperture 24 as small as possiblewhich improves the collection capability of the collector mirror 26. Forexample, the aperture 24 may be in the region of 0.5 mm in diameter.This provides an additional advantage as the resulting diffractionpattern gives rise to a light distribution following a Bessel functionwhich is particularly well adapted for scanning indicia.

The molded member 52 needs to be secured to the circuit board 14, and tothat end, snaps 62, 64 are provided. These automatically latch onto thecircuit board when the component is installed. Alternatively, posts onthe lower side of the molded member may protrude through the board to beheat-staked onto the bottom of the board. Ultrasonic staking could alsobe used.

The collector mirror 26 is coated with a reflective coating so thatlight impinging upon it will be reflected downwardly toward thephotodetector 40. This coating may also cover that part 62 of the moldedmember that serves as a housing for the photodiode. This will render theoptics assembly opaque in that area to prevent any light from reachingthe photodiode except via the aperture 36 and the filter 38.

This reflective coating may also serve another function. Typically, thecoating will be a thin film of metal such as gold, aluminum or chrome.These films are electrically conductive. Accordingly, the film also actsas an electromagnetic interference (EMI) shield for the photodiode 40.The use of a surface coating to protect the photodiode enables the usualEMI shield to be dispensed with, thereby eliminating both the cost of aseparate shield and the labor to have it installed within the assembly.

The coating is electrically grounded by extending a projection 66 of themolded member into a small socket 68 in the PCB. Alternatively, theprojection 66 could be press-fitted into a plated through-hole in theboard.

The housing portion 62 of the molded member 52 not only acts to hold theoptical filter 38 in place on top of the photodiode 40, but alsoentirely surrounds the photodiode, thereby preventing stray light fromreaching it. The aperture 36 in the housing may be small to limit thefield of view of the detector, maximizing ambient light immunity. Theaperture needs to be accurately located with respect to the collectormirror 26, to allow the use of a minimum-sized field of view. Accuraterelative positions of the aperture and the collector mirror are easilyachieved since they are molded as a single part.

An alternative arrangement is shown in FIG. 3. In certain circumstancesit is desired to provide an arrangement in which the beam 30 leaves theoptical assembly at an angle other than 90 to the vertical (relative tothe PCB 14). For example, there may be instances in which the mountingrequirements mean that the PCB 14 is mounted at a non-orthogonalposition. In previous arrangements it has been necessary to overcomethis problem by introducing additional spacers when mounting the PCB 14such that the beam 30 leaves at the desired angle. This problem issolved in the arrangement according to FIG. 3 by adjusting the angle bywhich the beam exits the optical assembly to compensate for the mountingangle and remove the need to mount the PCB including a spacer. In thearrangement shown, this is achieved by altering the angle of thescanning mirror assembly 28, which is of particular benefit as noadjustment of the laser mounting would be required. It will beappreciated that the remaining optics may also require adjustment tofurther compensate which adjustments can be easily achieved by theperson skilled in the art.

The angle involved is dependent on the particular consumer requirementsbut may be in the region of 45-90° to the PC board, more preferably inthe range of 60-70° and most preferably 65° to the PCB.

FIGS. 11 and 12 show an alternative optical assembly and motor driveembodiment to FIG. 3 according to an embodiment of the invention.Although illustrating two-dimensional scanning, the arrangement ofcomponents may also be configured for one-dimensional scanning alone.The arrangement is mounted on a single base board 500 and includes alaser assembly 502 of suitable type, for example, of the type discussedabove. In this embodiment, the laser assembly 502 may be mounted on thechassis including peripheral side 550, which also acts as a heat sinkfor the laser. A beam from the laser assembly 502 is not folded, butdirectly passes through an aperture 504 in a collector mirror 506 and isreflected by a scanning mirror 508. The returning beam isretro-reflected onto the collector mirror 506 and directed to a detectorof suitable known type 510.

Turning now to the drive assembly for the scanning mirror 508 in moredetail, the mirror is mounted in conjunction with a permanent magnet 512which interacts with a magnetic field provided by an AC current drivencoil 514 to oscillate the mirror. The mirror is mounted relative to thebase 500 via an attachment element 501 which is connected to the mirrorby two Mylar springs 518, 520. Although the mirror is mounted parallelto the base, the attachment element 516 is mounted at 25° to thehorizontal base and the Mylar springs which extend perpendicular to theattachment strip 516 are hence at 25° to the vertical. Accordingly ascanning plane is defined at 25° to the vertical as discussed in moredetail below. It will be appreciated, of course, that any appropriateangle can be selected. The scan angle is then defined by the amplitudeof motion of the mirror and is preferably selected to be 50°. The mirrorassembly is of the unbalanced type, that is, no counterweights areprovided against the mirror mass as considered relative to the point ofsupport.

The use of an unbalanced mirror, i.e., one in which no counterweightsare provided in the mirror assembly, is particularly suitable inimplementation in which the mirror is driven at a speed of greater than100 scans per second. With an unbalanced mirror, since the attachmentpoints of the mirror to the flexible springs are not the center of massof the mirror assembly, while the mirror is at rest, gravity will exerta relatively greater force on the side of the mirror assembly having thegreater mass, causing the mirror to “droop” on its heavier side and pullon the flexible springs. Of course, the effect of such force depends onthe orientation of the scanner with respect to the force vector ofgravity. The same “drooping” effect is present when the mirror isscanning at relatively low speeds, so in such applications the use of abalanced mirror would be preferred. A balanced mirror, however, requiresadditional mass be added to the mirror, or mirror assembly, which is adrawback in terms of operating design weight and consequently the powerrequirements.

In the embodiment of high speed operation (i.e., at more than 100 scansper second), the material composition, size, shape and thickness of thespring may be appropriately selected to achieve the desired resonantfrequency. For example, for operation at approximately 200 scans/second,the selection of a Mylar spring with a thickness of 4 mils isappropriate. For operation at 400 scans/second, a stainless steel springwith a thickness of about 3 mils is preferred.

It will be seen that the mirror 508 is angled relative to the verticalto direct the scanning beam out of the upper face of the assembly. Aswith FIG. 1, although the mirror 508 is represented in FIG. 11 as beingalso angled out of a plane orthogonal with a plane of the paper, this ismerely a drawing representation to render the figure clearer. It will beseen that the attachment element 516 includes limbs 522 and 524extending to either side of the Mylar springs 518, 520. These limbs arepositioned within shaped recesses in side blocks 526, 528 allowing acertain amount of clearance for the limbs which provides adequate spacefor the desired scanning angle to be achieved while providing stops tolimit the amount of oscillation of the mirror should a shock be impartedto the unit, for example, by dropping it.

Accordingly, a beam emitted by the laser assembly 502 incident on themirror 508 is swept through an angle of 50° by the scanning mirror.However, the plane of sweep of the beam (the scan plane) is not at 90°to the base 500 but is at an angle constrained by the direction in whichthe magnet is driven to oscillate, i.e., the axis of flexing of theMylar springs. This can be best be understood with reference to FIGS.13a and 13 b. In FIG. 13a the laser beam 30 enters in the Y direction.The mirror and drive assembly are not shown but in FIG. 13a the normalmirror configuration is assumed, that is, the mirror is angled at 45° tothe X-Z plane and is mounted to oscillate about the X direction. As aresult a scan plane 530 is established in the Y-Z plane. However in FIG.13b the mirror and mirror drive are mounted as discussed in relation toFIGS. 11 and 12. It will be seen, therefore, that the scan line isobtained in a plane 532 at 25° to the Y-Z plane. Again, any desired scanplane angle or scanning angle can be selected.

Accordingly a non-90° output angle of the beam as discussed in relationto FIG. 3 is achieved in a different manner.

FIG. 9 shows a second preferred embodiment in which two-dimensionalscanning motion is achieved by using two mirrors each oscillating in anorthogonal plane. Multi-pattern scanners can be achieved by using tworeflector X-Y motion as described in U.S. Pat. No. 5,581,070, No.5,637,856 and No. 5,614,706, all of which are incorporated herein byreference. Preferably, the two reflectors are driven by a thin flexibleelement-type drive of the type shown in FIG. 5a or FIG. 7. Inparticular, the optical module 10 emits a beam 30 through aperture 24 incollector 34 which is oscillated in a first direction, for example, theX direction by a first oscillating mirror 28 a mounted on a firstV-shaped element 84 and is then oscillated in a second direction, forexample, the Y direction by a second mirror 28 b mounted on a V-shapedband 84. As a result, any desired scanning pattern can be achieved atthe target as represented schematically by pattern 11.

All of the elements are preferably provided in a single module as can beseen from the base layout depicted in FIG. 10. In particular laser 18emits an outgoing beam 30 through an aperture 34 in collector mirror 26.The beam is oscillated in the X direction by mirror 28 a, and in the Ydirection by mirror 28 b, giving rise to a scanning pattern shownschematically at 11. The returning beam 32 returns along the reflectionpath and is directed onto the detector 40 by the collector mirror 26. Itwill of course be appreciated that the arrangement is preferably used inconjunction with the optical assembly shown in FIG. 1 and the exactpositioning and orientation of the parts will be apparent to the skilledreader.

FIG. 14 shows an alternative scan engine form factor and ergonomichousing variation for incorporation of the scanner described herein orany other suitably dimensioned scanner. In particular, the scanner isincorporated into a pen-type housing 600 having a scanning window 602.The pen-type housing 600 is preferably elongate having broad front andrear faces 604, 606 and narrow side faces. The scanning window ispreferably provided at the upper end of broad face 604, at the oppositeend to the pen “nib” 612. Scanning can be triggered by one or moretriggers 608, 610 provided, for example, on the side or front face ofthe pen housing 600. The pen nib 612 can either be a conventional pen oran electronic pen. Because of the broad faces, the arrangement easilyhouses a scanner module of the type described herein. In addition, thepositioning of the window 602 allows ergonomic scanning, and thepositioning of a plurality of triggers allows left- or right-handedusers to use the scanner with ease. It will be seen that the broad rearface 606 of the housing 600 contacts the user's palm in reading mode forcomfort and ease of use while in the writing mode the narrow side facecontacts the user's palm, so that the arrangement can be used normallyas a pen.

Although the window 602 is shown in FIG. 14 with its shorter sideparallel to the axis of the pen, alternatively the longer side may bepositioned parallel to the axis with the direction of the scan line alsoparallel to the axis of the pen.

Turning now to FIG. 15, the illustrated arrangement is similar to thatshown in FIG. 10 in which a laser 18, a collection mirror 26 having anaperture 24, a reciprocally oscillatable scan mirror 28, and a sensor 40are all mounted on a rectangular support such as printed circuit board14. The laser 18 emits a laser beam along a first optical path 30 athrough the aperture 24 to the scan mirror 28 for reflection therefrom.The collection mirror 26 reflects light impinging thereon along a secondoptical path 30 b to the sensor 40. The laser beam impinging on the scanmirror 28 is directed and swept along a third optical path 30 c to thesymbol for reflection therefrom. At least some of the light reflectedoff the symbol travels in a countercurrent direction along the thirdoptical path 30 c to impinge on the scan mirror 28 and is, in turn,reflected along a fourth optical path 30 d to the collection mirror 26.

The folded optical path makes for a very compact retro-reflective module10 whose rectangular parallelepiped form factor has dimensions less than20.6 mm×14.2 mm×11.4 mm. The laser 18 and sensor 40 are not located in aside-by-side relationship as in FIG. 1, but instead, are located atopposite end regions of the board 14.

FIG. 16 is identical to FIG. 15, except that the laser 18 does not emitits laser beam directly through the aperture 24, but instead, directsthe laser beam initially to a fold mirror 29 for reflection therefromthrough the aperture 24. The fold mirror 29 is a planar, reciprocallyoscillatable scan mirror, just like scan mirror 28, except smaller inarea. The fold mirror may be oscillated to sweep the laser beamreflected therefrom in a first scan direction. When operatively combinedwith the scan mirror 28 which sweeps the laser beam reflected therefromin a second scan direction, the symbol is read with a two-dimensionalscan pattern. Preferably, the first and second scan directions aremutually orthogonal.

This invention also contemplates that the fold mirror 29 be permanentlyfixed in position, in which event, the symbol is read with aone-dimensional scan pattern or a single scan line. Preferably, the foldmirror 29 is not permanently fixed, but instead, its drive is disabledduring a one-dimensional reading mode. Upon re-enabling the drive duringa two-dimensional reading mode, the two-dimensional scan pattern isgenerated. The disabling of the drive for the fold mirror may beachieved by the generation of a disabling control signal by themicroprocessor and/or by the depression of a control switch by a user.

It will be understood that each of the features described above, or twoor more together, may find a useful application in other types ofscanners and bar code readers differing from the types described above.

While the invention has been illustrated and described as embodied in ascanning assembly in compact bar mode readers, it is not intended to belimited to the details shown, since various modifications and structuralchanges may be made without departing in any way from the spirit andscope of the present invention. In particular it will be recognized thatfeatures described in relation to one embodiment can be incorporatedinto other embodiments as appropriate in a manner that will be apparentto the skilled reader.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim:
 1. In an electro-optical reader for directing a light beam to,and for detecting light reflected from, a bar code symbol to be read, aretro-reflective scan module, comprising: a) a generally planar,rectangular support; b) a light source supported by the support, forgenerating and directing the light beam along a first optical path; c) aselectively activatable first scan assembly including a generallyplanar, reciprocally oscillatable first scan mirror mounted in the firstoptical path for oscillating movement on the support to reflect thelight beam from the light source along a second optical path, and afirst drive for reciprocally oscillating the first scan mirror to sweepthe light beam in a first direction across the symbol; d) an opticalassembly mounted on the support, and including an optical element havinga light-collection portion for collecting and re-directing the lightreflected from the symbol, and a light-passage portion for allowing thelight beam along the second optical path to pass through thelight-collection portion; e) a second scan assembly including agenerally planar, reciprocally oscillatable second scan mirror mountedin the second optical path for oscillating movement on the support toreflect the light beam received from the light-passage portion to bedirected to the symbol, and also for simultaneously directly receivingthe light reflected from the symbol and for directing the receivedreflected light to the light-collection portion, the second scanassembly including a second drive for reciprocally oscillating thesecond scan mirror to sweep the light beam in a second directionorthogonal to the first direction across the symbol; f) a controlleroperatively connected to the drives, for actuating both of the drives tooscillate both scan mirrors to sweep the symbol with a multiple linescan pattern, and for selectively deactuating one of the drives to sweepthe symbol with a single line scan pattern; g) a sensor supported by thesupport, for detecting the collected reflected light re-directed by thelight-collection portion and for generating an electrical signalcorresponding to the symbol.
 2. The module as defined in claim 1,wherein the light-passage portion includes an aperture disposed in thelight-collection portion.
 3. The module as defined in claim 1, whereinthe first drive oscillates the first scan mirror to sweep the light beamacross the symbol at more than 30 times per second, said drive includinga flexible leaf spring on which the first scan mirror is mounted.
 4. Themodule as defined in claim 1, wherein the first drive includes anenergizable electromagnetic coil drive member and a permanent magneticdrive member in operational proximity thereto, for imparting a force tothe first scan mirror, thereby resulting in movement of the first scanmirror in an oscillating manner about an axis, and thereby causing thelight beam reflected off the first scan mirror to sweep along a scanningpath.
 5. The module as defined in claim 1, wherein the second driveincludes a flexible leaf spring on which the second scan mirror ismounted.
 6. The module as defined in claim 1, wherein the second driveincludes an energizable electromagnetic coil drive member and apermanent magnetic drive member in operational proximity thereto, forimparting a force to the second scan mirror, thereby resulting inmovement of the second scan mirror in an oscillating manner about anaxis, and thereby causing the light beam reflected off the second scanmirror to sweep along a scanning path.
 7. The module as defined in claim1, wherein the controller is operative for selectively disabling thefirst drive to malntain the first scan mirror in a stationary position.8. The module as defined in claim 1, wherein the light-collectionportion directs the light impinging thereon to the sensor along a thirdoptical path, and wherein the second scan mirror directs the lightimpinging thereon to the symbol along a fourth optical path that crossesthe third optical path.